X-ray tomographic apparatus has been marketed for many years for the purpose of conducting X-ray cranial tomography to obtain plural, evenly spaced X-ray cuts of a cranial site of interest such as the temporo-mandibular joint for example. In every case tomographic apparatus is positioned such that an X-ray head and an X-ray film cassette are positioned on opposite sides of the patient's anatomical site of interest. The X-ray head and film cassette are movable about the anatomical site of interest while the X-ray head is energized to achieve each tomographic image on the film such as being supported on a pivotally movable arm that is rotated about a pivot point. This pivotal motion blurs out all anatomy in front of and behind the pivot point and thus provides an X-ray exposure that is representative of a section taken through the anatomical site of interest. In many cases, depending upon the character of X-ray tomograph that is desired, the apparatus accomplishing rotary movement of the X-ray head and film holder will move either the X-ray head or film holder or both along an elliptical path such as substantially conforming to the configuration of the mandibular of the patient. This type of apparatus is widely utilized in dentistry and for maxillo-facial surgery although it has a number of other uses as well.
For the most part, the X-ray tomography apparatus that has been developed and marketed accomplishes rotation of the X-ray head and film support arm about a substantially vertical axis so that the arcuate movement of these components is in a substantially horizontal plane. U.S. Pat. Nos. 4,675,888 of Gastrin; 4,823,369 of Guenther, et al.; and 4,852,134 of Kinanen, et al. are representative of simple vertical axis rotation of an arm that supports the X-ray head and film holder. More complex rotary movement of a support for an X-ray head and film holder, including relative lateral movement during rotation is evidenced by U.S. Pat. Nos. 4,741,007 of Virta, et al.; 4,756,014 of Doebert; 4,783,793 of Virta, et al.; 4,811,372 of Doebert, et al.; 4,813,060 of Heubeck, et al.; 4,856,038 of Guenther, et al.; 4,907,251 of Mork, et al.; and 4,985,907 of Moteni. Although each of the U.S. Patents previously identified describe rotation of a support for an X-ray head and film holder about a vertical axis, one patent, namely U.S. Pat. No. 4,974,243 of McArdle, et al. discloses a positioning system for X-ray tomography including an X-ray head and film support arm or spar that rotates about a fixed horizontally oriented axis with respect to the '243 patent of McArdle, et al., it should be noted that the head fixator mechanism 50 includes an associated X, Y and Z positioning mechanism 52, thus, the head fixator or cephalostat is positionable utilizing X, Y and Z translational mechanisms representing adjustment in each of X, Y and Z cartesian coordinates.
Although X-ray tomography systems such as that shown by the '243 patent of McArdle, et al. are quite functional, nevertheless, they are for the most part of quite complicated design and function and therefore are quite expensive from the standpoint of purchase, installation and repair. It is desirable to provide X-ray tomography apparatus having characteristics of low cost, simplicity and yet being efficient from the standpoint of functionality.